This invention relates to nuclear reactor plants. It has particular relationship to the art of inspecting the primary tubes of steam generators of such a plant in instances where defects are suspected. While this invention is uniquely applicable to inspection of tubes of nuclear reactor plants, it may also find utility in the inspection of conventional steam generators and heat exchangers. To the extent that this invention is so applied, such application is regarded as within the scope of equivalents of this invention.
The primary tubes of the steam generator of a nuclear-reactor plant are typically composed of INCONEL alloy. Each tube is typically of U-shape having vertical members joined to a horizontal member by knees. Periodically the tubes are subject to eddy-current tests. The results of such tests indicate that a certain tube requires more detailed inspection and for this purpose parts of a tube must be severed from the remainder and inspected. The primary tubes of a steam generator which have been in service are radioactive. In addition it is undesirable that the tubes be subject to oxidation. For these reasons the tubes are maintained under water in the steam generator. To remove a part of a tube for inspection, it is necessary that remotely actuable tube-cutting apparatus be inserted in the water of the steam generator and perform the cutting in this radioactive environment.
It is frequently desirable that a tube to be inspected be severed. The severance is predominantly along a vertical member's arm but may also take place along the horizontal member or one of the knees. In some steam generators the tubes are confined in a region of limited dimension affording limited access for severing the vertical member of a tube. Grinding wheels or conventional cutters (see, for example, Hanaway U.S. Pat. No. 3,449,992) which are used, in accordance with the teachings of the prior art, in other steam generators, that afford clearance for such grinders or conventional cutters, cannot be used in the steam generators where the access is limited and there is no such clearance. Metal disintegration machining (MDM) has also been proposed. Such machining produces nickel oxide during the machining. The nickel oxide is deposited in the bottom of the steam generator and causes the tubes to crack.
Another problem encountered in attempting to sever the tubes is that they are closely packed: An attempt to cut a tube either along the horizontal member or the vertical members or along the knees between these members with a conventional cutter as disclosed by Hanaway would result in the cutting of several neighboring tubes.
It is an object of this invention to provide apparatus for severing selected primary tubes of a steam generator of a nuclear reactor plant, in which the clearance afforded for a cutter to cut selected tubes is limited and in which the primary tubes are closely packed, without contaminating the steam generator with nickel oxide or other contaminants resulting from cutting by metal disintegration machining or the like, and without cutting a number of tubes in the neighborhood of selected tubes.
It is another object of this invention to provide such apparatus for severing a selected tube either along a vertical members, or along the horizontal member or along the knees between the horizontal and vertical members.